The present invention relates to a system and method for controlling speed of a vehicle.
To enhance safety of a car and passengers in present-day road traffics, efforts are being made to support the operator in routine driving operations.
In this direction, antilock braking systems (ABS) have been proposed and adopted to enhance longitudinal vehicle stability in dynamically critical conditions in braking process.
xe2x80x9cAutomatic distance regulationxe2x80x9d (ADR) systems have been proposed that are intended to detect and carry out a controlled braking action to control the distance of a vehicle from other vehicles and/or stationary objects in the direction of vehicle motion. JP-A 7-144588 discloses a system whereby traveling speed and deceleration of a vehicle in front are determined using a Doppler sensor and a vehicle speed sensor, which are on a vehicle to be controlled, and a desired distance from the vehicle in front is determined in response comparison of the traveling speed of the vehicle in front with a predetermined value of 15 km/h. In this system, a driver is warned and an automatic braking action is initiated if the distance from the vehicle in front becomes less than the desired distance. JP-A 10-114237 discloses a technique to release ADR in response to operator acceleration request for passing a preceding vehicle in front without relying on detection of accelerator pedal position. Using a predetermined characteristic curve, a throttle position is estimated from a present position of the throttle actuator. The operator acceleration request is detected after comparison of a deviation of the actual throttle position from the estimated throttle position with a threshold value. The deviation becomes zero when the accelerator pedal is released, but the deviation exceeds the threshold value when the accelerator pedal is depressed.
Other systems have been proposed that are intended to initiate braking action before the operator of a vehicle initiates braking action. JP-A 6-24302 discloses a system whereby, when a foot of the operator leaves an accelerator pedal, two micro switches are both closed to energize a solenoid for activating a brake pedal. Energizing the solenoid pulls the brake pedal to partially activate a braking system before the foot of the operator is stepped on the brake pedal.
Commonly assigned co-pending U.S. patent application Ser. No. 09/640,792 filed on Aug. 18, 2000 discloses a preview brake control system for assisting vehicle operator braking action. For assisting vehicle operator braking action, a detection sub-system on a vehicle to be controlled detects obstacles, which are in or near the direction of motion of the vehicle, and provides corresponding environmental data to a brake controller. In addition, the vehicle has vehicle condition sensors for detecting parameters indicative of the condition or state of motion of the vehicle and transmitting corresponding data to the controller, and vehicle operator demand sensors for detecting parameters indicative of power or brake demand of the operator and transmitting corresponding data to the controller. From the data reported concerning the obstacles, the vehicle condition parameters and the operator demand parameters, the controller ascertains whether or not there is a need for operator braking action. The controller determines a stand-by braking torque in terms of a brake pressure and generates a braking signal for a braking sub-system or braking device to apply the stand-by braking torque to at least one or wheels of the vehicle. As sensors for detection of the obstacles located in or near the direction of motion of the vehicle, conventional radar sensors employing laser, whose application is familiar to those skilled in the art, are used. However, any other types of sensors that permit an adequate preview of the range of motion of the vehicle and which are suitable for service under rough vehicle condition may be used. For full description of the preview brake control system, U.S. patent application Ser. No. 09/640,792, which has its corresponding European Patent Application No. 00307108.1 filed on Aug. 18, 2000, has been hereby incorporated by reference in its entirety.
If both the preview brake control system and an ADR system are installed in a vehicle, there would be a need to avoid application of an additional torque (positive torque) to a wheel or wheels of a vehicle when a stand-by braking torque (negative torque) is applied to the wheels. Application of the stand-by braking torque continues for a predetermined time since determination of a need for operator braking action. Let us consider the case where immediately after the vehicle has approached a preceding vehicle, the stand-by braking torque is applied corresponding to a need for vehicle operator braking action. Under this condition, the ADR system is put into operation before the preceding vehicle shifts to the next lane. Then, the ADR system requests an additional torque to increase speed of the vehicle toward a set cruising speed because the lane has been cleared. If the additional torque is applied immediately to wheel or wheels of the vehicle against the stand-by braking torque, there may occur shocks when the stand-by braking torque disappears upon elapse of the predetermined time. Such shocks are objectionable to the operator.
There would be another need to terminate application of a stand-by braking torque in response to vehicle operator acceleration request for passing a preceding vehicle by shifting to the next lane after having approached to the preceding vehicle quickly enough to initiate application of the stand-by braking torque.
It is an object of the present invention to provide a system and method for controlling speed of a vehicle, which has met at least one of the above-mentioned needs.
In carrying out the above object and other objects, advantages, and features of the present invention, a system for controlling speed of a vehicle is provided, which comprises a prime mover coupled to at least one wheel of the vehicle for applying a positive torque to the at least one wheel in response to an accelerating signal; and a controller having a control logic for determining an actual distance from a preceding vehicle in front, comparing the actual distance to a set desired distance to determine whether the actual distance is greater than the desired distance, determining whether or not a stand-by braking torque is applied to the at least one wheel, determining an additional torque requested by an automatic distance regulation (ADR) to increase vehicle speed when the actual distance is greater than the desired distance and the stand-by braking torque is not applied, and generating an accelerating signal for the prime mover to apply the additional torque to the at least one wheel.